1. Field of the Invention
The present invention relates to the field of scientific instrumentation. More specifically, the present invention relates to pipettes and array pipetters.
2. Description of the Related Art
The widespread adoption by the biotech, pharmaceutical, and life science industry of 96-well plates and its denser 384- and 1536-well descendants has stimulated the concomitant demand for pipetters that can take advantage of these formats. Indeed, there are a variety of fluid-handling devices on the market that are designed to pipette in and out of 96 or 384 wells simultaneously. These array pipetters have 96 or 384 tips arranged in rectangular arrays of 8×12 or 16×24, with 9-mm or 4.5-mm pitch, respectively. There are also devices that only address one column of the plate at a time; this allows for more flexibility at the cost of reduced throughput.
Array pipetters typically are volume displacement devices designed to work in the aspirate-and-dispense mode. Typically a tip, or cannula, is mated to a piston-and-barrel structure with appropriate seals to achieve air-tightness. As the piston moves up, liquid is drawn into the cannula. As the piston moves down, liquid is expelled from the same cannula. This combination of a cannula and piston-barrel is repeated across the array (e.g., 96 or 384 times) to give a pipetting head. For convenience, the cannulae are often assembled into a single tip-carrier to facilitate exchanging one set for another.
This basic design has proved its worth in terms of simplicity, manufacturability, robustness, and versatility. It is adopted by virtually all manufacturers of array pipetters. Yet it suffers from one major defect. Once a reagent has been delivered, the only way to clean out the cannulae is by repeated aspiration and dispensing of a cleaning fluid. Sometimes, sonication is applied to ameliorate the cleaning action. The inside of the cannulae can also be coated with Teflon to reduce adhesion. Despite all these measures, currently available cleaning methods are often not thorough enough and carry-over of reagents becomes a significant problem. When carry-over of reagents must be limited to an absolute minimum, the only existing solution is to replace fixed cannulae with disposable pipette tips. While this is a workable solution, it entails significant cost increases. In addition, throughput is decreased because replacing an entire tip-array is time consuming, especially since it must usually be done manually.